Electrical energy storage system and energy storage system

ABSTRACT

An electrical energy storage system is provided in this dislosure, which includes: M battery packs; M first DC/DC converters, where first terminals of the M first DC/DC converters are respectively connected to the M battery packs, the M first DC/DC converters are classified into N first DC/DC converter sets; and N second DC/DC converters, where the N second DC/DC converters one-to-one correspond to the N first DC/DC converter sets, a first terminal of each second DC/DC converter is connected to second terminals of all first DC/DC converters in a first DC/DC converter set corresponding to the second DC/DC converter, a second terminal of each second DC/DC converter is connected to a first interface of the electrical energy storage system, the first interface is to receive a direct current from a power generation system or output a direct current to the power generation system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2020/096468, filed on Jun. 17, 2020, which is hereby incorporatedby reference in its entirety.

TECHNICAL FIELD

This dislosure relates to the power supply field, and in particular, toan electrical energy storage system and an energy storage system.

BACKGROUND

An electrical energy storage system may store electrical energygenerated by a power generation system in a battery, and obtainelectricity from the battery when needed. The power generation systemmay be a new energy power generation system, for example, a wind powergeneration system or a photovoltaic power generation system.

The power generation system may output a direct current or analternating current. The direct current may be supplied to theelectrical energy storage system for storage, and the alternatingcurrent is used to be supplied to an alternating current power grid oran alternating current load. An alternating current voltage that isoutput by the power generation system includes different voltage levels.For example, the alternating current voltage levels usually may includesingle-phase 220 Vac and three-phase 380 Vac. After alternating currentto direct current (AC/DC) is performed on alternating current voltagesof different levels to obtain direct current voltages, magnitudes of thedirect current voltages also vary greatly. For example, the single-phase220 Vac corresponds to a direct current voltage 311 Vdc, and thethree-phase 380 Vac corresponds to a direct current voltage 537 Vdc. Vacrepresents a maximum magnitude value of an alternating current voltage,and Vdc represents a magnitude of a direct current voltage.

A direct current to direct current (DC/DC) converter in the electricalenergy storage system is configured to: receive a direct current that isoutput by the power generation system, and input the direct current to abattery pack for storage after performing direct current voltageconversion. Therefore, the DC/DC converter needs to be designed, so thatan input voltage range of the DC/DC converter adapts to an outputvoltage range of the power generation system.

In a conventional technology, an input voltage range of a DC/DCconverter in an electrical energy storage system is usually designed tomatch a voltage level of an alternating current of a power generationsystem. However, in some scenarios, if the alternating current voltagelevel of the power generation system changes, for example, changes fromsingle-phase 220 Vac to three-phase 380 Vac, the DC/DC converter cannotsupport an input voltage range corresponding to the three-phase 380 Vacbecause the input voltage range of the DC/DC converter is designed tosupport the single-phase 220 Vac. Consequently, the electrical energystorage system cannot support different voltage levels, and applicationflexibility of the electrical energy storage system is affected.

SUMMARY

This disclosure provides an electrical energy storage system and anenergy storage system, to improve application flexibility of theelectrical energy storage system.

According to a first aspect, an electrical energy storage system isprovided. The system includes: M battery packs; M first direct currentto direct current (DC/DC) converters, where first terminals of the Mfirst DC/DC converters are respectively connected to the M batterypacks, the M first DC/DC converters are classified into N first DC/DCconverter sets, M is an integer greater than 1, and N is an integergreater than 0; and N second DC/DC converters, where the N second DC/DCconverters one-to-one correspond to the N first DC/DC converter sets, afirst terminal of each second DC/DC converter is connected to secondterminals of all first DC/DC converters in a first DC/DC converter setcorresponding to the second DC/DC converter, a second terminal of eachsecond DC/DC converter is connected to a first interface of theelectrical energy storage system, the first interface is configured toreceive a direct current from a power generation system or output adirect current to the power generation system, and N is an integergreater than 1.

In this embodiment of this dislosure, the electrical energy storagesystem includes two types of DC/DC converters, and the N second DC/DCconverters are disposed between the power generation system and thefirst DC/DC converters. When an output voltage range of the powergeneration system does not match an input voltage range of the firstDC/DC converter and a battery is charged, the second DC/DC converter maybe configured to perform voltage conversion on a voltage input by thepower generation system, so that an output voltage adapts to the inputvoltage range of the first DC/DC converter. When the battery isdischarged, the second DC/DC converter may perform voltage conversion ona voltage input by the first DC/DC converter, so that a range ofvoltages output to the power generation system adapts to a voltage levelof the power generation system. Therefore, the electrical energy storagesystem can support different voltage levels of the power generationsystem, thereby improving application flexibility of the electricalenergy storage system.

In this embodiment of this dislosure, because the electrical energystorage system can support different voltage levels of the powergeneration system, the electrical energy storage system can adapt toinverters of different voltage levels in the power generation system. Inother words, in production processes of the electrical energy storagesystem and the power generation system, because the electrical energystorage system can adapt to power generation systems of differentvoltage levels, the electrical energy storage system corresponding tothe power generation systems of different voltage levels can be producedby using a unified standard, thereby improving the productionefficiency.

With reference to the first aspect, in a possible implementation of thefirst aspect, when Vinv−Vbus>Vth and a battery pack is discharged, thesecond DC/DC converter is configured to boost Vbus to output Vinv; orwhen Vinv−Vbus>Vth and a battery pack is charged, the second DC/DCconverter is configured to buck Vinv to output Vbus, where Vinvrepresents a rated voltage of the second terminal of the second DC/DCconverter, Vbus represents a rated voltage of the first terminal of thesecond DC/DC converter, and Vth represents a preset threshold voltage.

With reference to the first aspect, in a possible implementation of thefirst aspect, when −Vth<Vinv−Vbus<Vth, the second DC/DC converter worksin a direct mode, where Vinv represents the rated voltage of the secondterminal of the second DC/DC converter, Vbus represents the ratedvoltage of the first terminal of the second DC/DC converter, and Vthrepresents the preset threshold voltage.

With reference to the first aspect, in a possible implementation of thefirst aspect, when Vinv−Vbus<−Vth and the battery pack is discharged,the second DC/DC converter is configured to buck Vbus to output Vinv; orwhen Vinv−Vbus>Vth and the battery pack is charged, the second DC/DCconverter is configured to boost Vinv to output Vbus, where Vinvrepresents the rated voltage of the second terminal of the second DC/DCconverter, Vbus represents the rated voltage of the first terminal ofthe second DC/DC converter, and Vth represents the preset thresholdvoltage.

With reference to the first aspect, in a possible implementation of thefirst aspect, when Vbus>Vbat and the battery pack is discharged, thefirst DC/DC converter is configured to boost Vbat to output Vbus; orwhen Vbus>Vbat and the battery pack is charged, the first DC/DCconverter is configured to buck Vbus to output Vbat, where Vbusrepresents the rated voltage of the first terminal of the second DC/DCconverter, and Vbat represents a rated voltage of an anode of thebattery pack.

With reference to the first aspect, in a possible implementation of thefirst aspect, when Vbus=Vbat, the first DC/DC converter works in thedirect mode, where Vbus represents the rated voltage of the firstterminal of the second DC/DC converter, and Vbat represents the ratedvoltage of the anode of the battery pack.

With reference to the first aspect, in a possible implementation of thefirst aspect, when Vbus<Vbat and the battery pack is discharged, thefirst DC/DC converter is configured to buck Vbat to output Vbus; or whenVbus<Vbat and the battery pack is charged, the first DC/DC converter isconfigured to boost Vbus to output Vbat, where Vbus represents the ratedvoltage of the first terminal of the second DC/DC converter, and Vbatrepresents the rated voltage of the anode of the battery pack.

With reference to the first aspect, in a possible implementation of thefirst aspect, the power generation system includes an inverter, a firstterminal of the inverter is connected to the first interface of theelectrical energy storage system, and a second terminal of the inverteris connected to an alternating current load or an alternating currentpower grid.

With reference to the first aspect, in a possible implementation of thefirst aspect, the power generation system is a photovoltaic powergeneration system, the power generation system includes a photovoltaicinverter, the photovoltaic inverter includes a maximum power pointtracking (MPPT) module and a DC/AC converter, and the inverter is theDC/AC converter; and a first terminal of the DC/AC converter isconnected to the first interface of the electrical energy storagesystem, the first terminal of the DC/AC converter is further connectedto the MPPT module, and a second terminal of the DC/AC converter isconnected to the alternating current load or the alternating currentpower grid.

According to a second aspect, an energy storage system is provided. Thesystem includes the electrical energy storage system according to thefirst aspect and a power generation system.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an application scenario according to anembodiment of this application;

FIG. 2 is a schematic diagram of an application scenario according to anembodiment of this application;

FIG. 3 is a schematic diagram of an application scenario according to anembodiment of this application;

FIG. 4 is a schematic diagram depicting a structure of an energy storagesystem according to an embodiment of this dislosure;

FIG. 5 is a schematic diagram of control logic of an electrical energystorage system 100 according to an embodiment of this dislosure;

FIG. 6 is a schematic diagram of control logic of an electrical energystorage system 100 according to an embodiment of this dislosure; and

FIG. 7 is a schematic diagram depicting a structure of an energy storagesystem according to an embodiment of this dislosure.

DESCRIPTION OF EMBODIMENTS

The following describes the technical solutions of this dislosure withreference to the accompanying drawings.

For ease of understanding the solutions of the embodiments of thisdislosure, several terms used in the embodiments of this dislosure arefirst described.

FIG. 1 is a schematic diagram of an application scenario according to anembodiment of this dislosure. As shown in FIG. 1, a power generationsystem 200 may generate an alternating current or a direct current, andsupply the alternating current to an alternating current power grid oran alternating current load. The power generation system 200 may furthersupply the generated direct current to an electrical energy storagesystem 100, and the electrical energy storage system 100 storeselectrical energy. When power needs to be supplied to the alternatingcurrent load, the electrical energy storage system 100 may output adirect current to the power generation system 200. After a directcurrent to alternating current (DC/AC) converter in the power generationsystem 200 processes the direct current, an alternating current isobtained and supplied to the alternating current load or the alternatingcurrent power grid.

Optionally, the power generation system 200 may be a new energy powergeneration system, for example, a wind power generation system or aphotovoltaic power generation system.

Optionally, the power generation system 200 includes a power generationmodule, and the power generation module may generate a direct current oran alternating current. For example, a power generation module in a windpower generation system usually generates an alternating current, and apower generation module in a photovoltaic power generation systemusually generates a direct current.

Optionally, the power generation system 200 further includes a voltageregulator module, and the voltage regulator module may regulate avoltage output by the power generation module. If a current output bythe power generation module is an alternating current, the voltageregulator module is further configured to convert the alternatingcurrent into a direct current. For example, a voltage regulator modulein a wind power generation system is usually an AC/DC converter, and avoltage regulator module in a photovoltaic power generation system isusually a DC/DC converter. For example, the DC/DC converter may bedisposed in a maximum power point tracking (MPPT) module in aphotovoltaic inverter (referring to FIG. 2).

Optionally, the power generation system 200 further includes aninverter. The inverter is usually disposed between the voltage regulatormodule and the alternating current load (or the alternating currentpower grid), and can implement direct current to alternating currentconversion. The inverter may also be referred to as a DC/AC converter.

The inverter includes a first terminal A1 and a second terminal A2. Thefirst terminal A1 is configured to receive a direct current, and thesecond terminal A2 is connected to the alternating current load or thealternating current power grid. The inverter may implement DC/ACconversion in a direction from the first terminal A1 to the secondterminal A2, and supply an obtained alternating current to thealternating current load or the alternating current power grid.

Optionally, the first terminal A1 of the inverter is further connectedto a first interface F of the electrical energy storage system 100 tooutput a direct current to the electrical energy storage system 100.

Optionally, the inverter may alternatively implement AC/DC conversion ina direction from the second terminal A2 to the first terminal A1. Forexample, when the power generation system 200 is connected to thealternating current power grid, an alternating current input by thealternating current power grid may be converted into a direct current,and the direct current is supplied to the electrical energy storagesystem 100.

For example, in the photovoltaic power generation system, the invertermay be a DC/AC converter in a photovoltaic inverter (referring to FIG.2).

FIG. 2 is a schematic diagram of an application scenario according to anembodiment of this dislosure. The scenario in FIG. 2 may be applied to aphotovoltaic power generation scenario.

As shown in FIG. 2, the application scenario includes a power generationsystem 200 and an electrical energy storage system 100. The powergeneration system 200 includes a photovoltaic (PV) component and aphotovoltaic inverter.

The photovoltaic inverter is a special inverter designed for thephotovoltaic power generation system. A core of photovoltaic powergeneration is to convert solar energy into electrical energy by using aphotovoltaic component (namely, a solar energy battery panel). However,because the photovoltaic component can generate only a direct current,the photovoltaic inverter needs to convert the direct current into analternating current to facilitate transmission and use of the electricalenergy.

Compared with an ordinary inverter, in addition to a DC/AC converter,the photovoltaic inverter further includes an MPPT module. The MPPTmodule includes a DC/DC converter. The MPPT module may be configured totrack a maximum voltage current value, so that the power generationsystem 200 outputs a current at a maximum power.

Optionally, the MPPT module and the DC/DC module in the photovoltaicinverter may be disposed in a same encapsulation component, or may bedisposed in different encapsulation components.

After performing voltage conversion on a direct current generated by thePV component, the MPPT module may output the direct current to theelectrical energy storage system 100. A first terminal A1 of the DC/ACconverter may be connected to the MPPT module and the electrical energystorage system 100, and a second terminal A2 of the DC/AC converter isconnected to an alternating current power grid or an alternating currentload to convert a direct current output by the MPPT module or theelectrical energy storage system 100 into an alternating current andsupply the alternating current to the alternating current load or thealternating current power grid.

The electrical energy storage system 100 generally includes one or moreDC/DC converters, one or more battery packs, and one or more batterymanagement systems (BMSs). Each battery pack corresponds to one BMS. TheBMS is usually configured to implement functions such as dynamicmonitoring of charging and discharging of a battery, battery balancing,and state of charge evaluation of the battery. A specific structure ofthe electrical energy storage system 100 continues to be described belowwith reference to the accompanying drawings.

FIG. 3 is a schematic diagram of an application scenario according toanother embodiment of this dislosure. The scenario in FIG. 3 may beapplied to a wind power generation scenario.

As shown in FIG. 3, the application scenario includes a power generationsystem 200 and an electrical energy storage system 100. The powergeneration system 200 includes a fan system, an AC/DC converter, and aDC/AC converter (namely, an inverter).

The fan system is configured to generate an alternating current. TheAC/DC converter may be configured to: convert the alternating currentgenerated by the fan system into a direct current, and implement avoltage regulation function. The AC/DC converter may further output thedirect current to the electrical energy storage system 100, so that theelectrical energy storage system 100 stores the electrical energy. TheDC/AC converter may be configured to: receive the direct current outputby the AC/DC converter, convert the received direct current into analternating current, and supply the alternating current to analternating current load or an alternating current power grid. The DC/ACconverter may further be configured to: receive a direct current outputby the electrical energy storage system 100, convert the received directcurrent into an alternating current, and supply the alternating currentto the alternating current load or the alternating current power grid.

It should be understood that the scenarios shown in FIG. 1 to FIG. 3 aremerely examples, but are not limitations. The electrical energy storagesystem and the energy storage system in the embodiments of thisdislosure may further be applied to an application scenario of anotherpower generation type.

FIG. 4 is a schematic diagram depicting a structure of an energy storagesystem according to an embodiment of this dislosure. The energy storagesystem includes a power generation system 200 and an electrical energystorage system 100.

As shown in FIG. 4, the electrical energy storage system 100 includes: Mbattery packs, M first DC/DC converters (expressed as DC/DC_1 in thefigure), N second DC/DC converters (expressed as DC/DC_2 in the figure),and M BMSs, where M is an integer greater than 1 and N is an integergreater than 0.

The M battery packs one-to-one correspond to the M BMSs. Each BMS isconfigured to manage a corresponding battery pack, for example, performfunctions such as dynamic monitoring of charging and discharging of abattery of the battery pack, battery balancing, and state of chargeevaluation of the battery.

The M battery packs one-to-one correspond to the M first DC/DCconverters. Each battery pack is connected to a first terminal of acorresponding first DC/DC converter.

The M first DC/DC converters may be classified into N first DC/DCconverter sets. The N first DC/DC converter sets one-to-one correspondto the N second DC/DC converters. Each first DC/DC converter setincludes one or more first DC/DC converters. Different first DC/DCconverter sets may include a same quantity of first DC/DC converters ordifferent quantities of first DC/DC converters.

Correspondingly, the M battery packs are classified into N battery packsets. The N battery pack sets, the N first DC/DC converter sets, and theN second DC/DC converters are in a one-to-one correspondence mutually.

Optionally, a first terminal of each of the N second DC/DC converters isconnected to second terminals of all first DC/DC converters in a firstDC/DC converter set corresponding to the second DC/DC converter.

A second terminal of each second DC/DC converter is connected to a firstinterface F of the electrical energy storage system 100, the firstinterface F is configured to receive a direct current from the powergeneration system 200 or output a direct current to the power generationsystem 200, and N is an integer greater than 1.

Optionally, the first terminal and the second terminal of the firstDC/DC converter each include two terminals: a positive terminal and anegative terminal. For example, the positive terminal and the negativeterminal of the first terminal of the first DC/DC converter arerespectively connected to an anode and a cathode of a battery pack.

Optionally, the first terminal and the second terminal of the secondDC/DC converter each include two terminals: a positive terminal and anegative terminal.

In some examples, the first interface F is connected to a first terminalA1 of an inverter in the power generation system 200.

The first DC/DC converter and the second DC/DC converter each canimplement a bidirectional boost or buck function. The first DC/DCconverter and the second DC/DC converter may further work in a directmode. In the direct mode, the first DC/DC converter and the second DC/DCconverter do not execute a boost/buck function, and are equivalent toone power switch.

Optionally, it may be understood that the N second DC/DC converters areconnected in parallel. When one of the N first DC/DC converter setsincludes a plurality of first DC/DC converters, the first DC/DCconverters in the set are connected in parallel.

Optionally, the first DC/DC converter may use an isolated powerconversion manner, or may use a non-isolated power conversion manner.

Optionally, the second DC/DC converter may use an isolated powerconversion manner, or may use a non-isolated power conversion manner.

Isolated power conversion means that a transformer is disposed in aDC/DC converter. Non-isolated power conversion means that no transformeris disposed in a DC/DC converter.

Optionally, in this embodiment of this dislosure, battery packs indifferent battery pack sets may be of a same model, or may bemanufactured by different vendors or may be of different models. Inother words, the electrical energy storage system in this embodiment ofthis dislosure may support different types of battery packs.

As shown in FIG. 4, the power generation system 200 includes theinverter (namely, a DC/AC converter), the first terminal A1 of theinverter is connected to the first interface F of the electrical energystorage system 100, and a second terminal A2 of the inverter isconnected to an alternating current load or an alternating current powergrid. The inverter may output a direct current to the electrical energystorage system 100 through the first interface F of the electricalenergy storage system 100.

Optionally, the power generation system 200 may be a new energy powergeneration system, for example, a wind power generation system or aphotovoltaic power generation system.

The power generation system 200 may further be connected to thealternating current power grid. An alternating current supplied by thealternating current power grid may be rectified by using the inverter inthe power generation system 200 to obtain a direct current, and thedirect current is supplied to the electrical energy storage system 100.

Optionally, the power generation system 200 further includes a powergeneration module and a voltage regulator module. The power generationmodule is configured to generate a direct current or an alternatingcurrent. The direct current or the alternating current becomes a directcurrent after passing through the voltage regulator module. The firstterminal A1 of the inverter is configured to receive a direct currentoutput by the voltage regulator module. The inverter may implement DC/ACconversion in a direction from the first terminal A1 to the secondterminal A2, and supply an obtained alternating current to thealternating current load.

Optionally, the inverter may alternatively implement AC/DC conversion ina direction from the second terminal A2 to the first terminal A1. Forexample, when the power generation system 200 is connected to thealternating current power grid, an alternating current input by thealternating current power grid may be converted into a direct current,and the direct current is supplied to the electrical energy storagesystem 100.

Optionally, if the power generation system 200 is a photovoltaic powergeneration system, the power generation module may include a PVcomponent. In this case, the inverter may be a DC/AC converter in aphotovoltaic inverter, and the voltage regulator module is an MPPTmodule in the photovoltaic inverter.

In this embodiment of this dislosure, the electrical energy storagesystem includes two types of DC/DC converters, and the N second DC/DCconverters are disposed between the power generation system 200 and thefirst DC/DC converters. When an output voltage range of the powergeneration system 200 does not match an input voltage range of the firstDC/DC converter and a battery is charged, the second DC/DC converter maybe configured to perform voltage conversion on a voltage input by thepower generation system, so that an output voltage adapts to the inputvoltage range of the first DC/DC converter. When the battery isdischarged, the second DC/DC converter may perform voltage conversion ona voltage input by the first DC/DC converter, so that a range ofvoltages output to the power generation system adapts to a voltage levelof the power generation system. Therefore, the electrical energy storagesystem can support different voltage levels of the power generationsystem, thereby improving application flexibility of the electricalenergy storage system.

In this embodiment of this disclosure, because the electrical energystorage system can support different voltage levels of the powergeneration system, the electrical energy storage system can adapt toinverters of different voltage levels in the power generation system. Inother words, in production processes of the electrical energy storagesystem and the power generation system, because the electrical energystorage system can adapt to power generation systems of differentvoltage levels, the electrical energy storage system corresponding tothe power generation systems of different voltage levels can be producedby using a unified standard, thereby improving the productionefficiency.

In this embodiment of this disclosure, a manner in which a plurality ofbattery packs are connected in parallel is used in the electrical energystorage system. Therefore, when a battery pack is invalid, normal workof another battery pack is not affected, thereby improving reliabilityof the electrical energy storage system.

FIG. 5 is a schematic diagram of control logic of an electrical energystorage system 100 according to an embodiment of this disclosure. Withreference to FIG. 4 and FIG. 5, it is assumed that Vbus represents arated voltage of a first terminal of any second DC/DC converter (inother words, a rated voltage of a second terminal of a first DC/DCconverter), and Vbat represents a rated voltage of a battery pack (inother words, a rated voltage of a first terminal of the first DC/DCconverter). The rated voltage may be an optimal voltage at whichelectrical equipment works normally for a long time. In this case,control logic of the first DC/DC converter is as follows:

When Vbus>Vbat, if the battery pack is discharged, the first DC/DCconverter is configured to boost Vbat to output Vbus; or if the batterypack is charged, the first DC/DC converter is configured to buck Vbus tooutput Vbat.

When Vbus=Vbat, the first DC/DC converter works in a direct mode.

When Vbus<Vbat, if the battery pack is discharged, the first DC/DCconverter is configured to buck Vbat to output Vbus; or if the batterypack is charged, the first DC/DC converter is configured to boost Vbusto output Vbat.

In an example, it is assumed that Vbus=350 Vdc and Vbat=48 Vdc. That is,Vbus>Vbat. In this case, when the battery pack is discharged, the firstDC/DC converter is configured to boost Vbat to output Vbus; or when thebattery pack is charged, the first DC/DC converter is configured to buckVbus to output Vbat.

FIG. 6 is a schematic diagram of control logic of an electrical energystorage system 100 according to an embodiment of this dislosure. Withreference to FIG. 4 and FIG. 6, it is assumed that Vinv represents arated voltage of a second terminal of any second DC/DC converter (inother words, a rated voltage at a first interface F), Vbus represents arated voltage of a first terminal of any second DC/DC converter (inother words, a rated voltage of a second terminal of a first DC/DCconverter), and Vth represents a preset threshold voltage. In this case,control logic of the second DC/DC converter is as follows:

When Vinv−Vbus>Vth, if a battery pack is discharged, the second DC/DCconverter is configured to boost Vbus to output Vinv; or if a batterypack is charged, the second DC/DC converter is configured to buck Vinvto output Vbus.

When −Vth<Vinv−Vbus<Vth, the second DC/DC converter works in a directmode.

When Vinv−Vbus<−Vth, if a battery pack is discharged, the second DC/DCconverter is configured to buck Vbus to output Vinv; or if a batterypack is charged, the second DC/DC converter is configured to boost Vinvto output Vbus.

Optionally, a specific value of Vth may be determined based on practice.For example, the specific value of Vth may be related to an inputvoltage range of the first DC/DC converter. When Vinv ∈[Vbus−Vth,Vbus+Vth], Vinv falls within the input voltage range of the first DC/DCconverter. Therefore, the second DC/DC converter works in a direct mode,and Vinv may be directly used as an input voltage of the second DC/DCconverter. For example, Vth is 5 V or 10 V.

In an example, it is assumed that Vinv=1000 V, Vbus=350 V, and Vth=10 V.That is, Vinv−Vbus>Vth. When the battery pack is discharged, the secondDC/DC converter is configured to boost Vbus to output Vinv; or when thebattery pack is charged, the second DC/DC converter is configured tobuck Vinv to output Vbus.

FIG. 7 is a schematic diagram depicting a structure of an energy storagesystem according to an embodiment of this dislosure. The energy storagesystem includes an electrical energy storage system 100 and a powergeneration system 200. The power generation system 200 in FIG. 7 is aphotovoltaic power generation system.

As shown in FIG. 7, the power generation system 200 includes aphotovoltaic inverter. The photovoltaic inverter includes an MPPT moduleand a DC/AC converter. The inverter in FIG. 4 may be the DC/ACconverter, and the voltage regulator module may be the MPPT module. Afirst terminal A1 of the DC/AC converter is connected to a firstinterface F of the electrical energy storage system 100, and the firstterminal A1 of the DC/AC converter is further connected to the MPPTmodule to receive a direct current from a photovoltaic (PV) component. Asecond terminal A2 of the DC/AC converter is connected to an alternatingcurrent load or an alternating current power grid.

The DC/AC converter may receive a direct current output by the MPPTmodule, implement DC/AC conversion in a direction from the firstterminal A1 to the second terminal A2, and supply an obtainedalternating current to the alternating current load.

Optionally, the first terminal A1 of the DC/AC converter is furtherconfigured to output a direct current to the electrical energy storagesystem 100 through the first interface F.

Optionally, the DC/AC converter may alternatively implement AC/DCconversion in a direction from the second terminal A2 to the firstterminal A1. For example, when the power generation system 200 isconnected to the alternating current power grid, an alternating currentinput by the alternating current power grid may be converted into adirect current, and the direct current is supplied to the electricalenergy storage system 100.

A function of the electrical energy storage system 100 is similar tothat in FIG. 4. For brevity, details are not described herein again.

A person of ordinary skill in the art may be aware that units,algorithms, and steps in the examples described with reference to theembodiments disclosed in this specification can be implemented byelectronic hardware or a combination of computer software and electronichardware. Whether the functions are performed by hardware or softwaredepends on particular applications and design constraint conditions ofthe technical solutions. A person skilled in the art may use differentmethods to implement the described functions for each particularapplication, but it should not be considered that the implementationgoes beyond the scope of this dislosure.

It may be clearly understood by a person skilled in the art that, forthe purpose of convenient and brief description, for a detailed workingprocess of the foregoing system, apparatus, and unit, refer to acorresponding process in the method embodiments. Details are notdescribed herein again.

In the several embodiments provided in this dislosure, it should beunderstood that the disclosed system, apparatus, and method may beimplemented in other manners. For example, the described apparatusembodiment is merely an example. For example, the unit division ismerely logical function division and may be other division in actualimplementation. For example, a plurality of units or components may becombined or integrated into another system, or some features may beignored or not performed. In addition, the displayed or discussed mutualcouplings or direct couplings or communication connections may beimplemented through some interfaces. The indirect couplings orcommunication connections between the apparatuses or units may beimplemented in electronic, mechanical, or other forms.

The units described as separate parts may or may not be physicallyseparate, and parts displayed as units may or may not be physical units,may be located in one position, or may be distributed on a plurality ofnetwork units. Some or all of the units may be selected depending onactual requirements to achieve the objectives of the solutions in theembodiments.

In addition, functional units in the embodiments of this dislosure maybe integrated into one processing unit, or each of the units may existalone physically, or two or more units are integrated into one unit.

When the functions are implemented in a form of a software functionalunit and sold or used as an independent product, the functions may bestored in a computer-readable storage medium. Based on such anunderstanding, the technical solutions of this dislosure essentially, orthe part contributing to the conventional technology, or some of thetechnical solutions may be implemented in a form of a software product.The computer software product is stored in a storage medium, andincludes several instructions for instructing a computer device (whichmay be a personal computer, a server, or a network device) to performall or some of the steps of the methods described in the embodiments ofthis dislosure. The foregoing storage medium includes any medium thatcan store program code, such as a USB flash drive, a removable harddisk, a read-only memory (ROM), a random access memory (RAM), a magneticdisk, or an optical disc.

The foregoing descriptions are merely specific implementations of thisdislosure, but are not intended to limit the protection scope of thisdislosure. Any variation or replacement readily figured out by a personskilled in the art within the technical scope disclosed in thisdislosure shall fall within the protection scope of this dislosure.Therefore, the protection scope of this dislosure shall be subject tothe protection scope of the claims.

What is claimed is:
 1. An electrical energy storage system, comprising:M battery packs; M first direct current to direct current (DC/DC)converters, wherein first terminals of the M first DC/DC converters arerespectively connected to the M battery packs, the M first DC/DCconverters are classified into N first DC/DC converter sets, M is aninteger greater than 1, and N is an integer greater than 0; and N secondDC/DC converters, wherein the N second DC/DC converters one-to-onecorrespond to the N first DC/DC converter sets, a first terminal of eachsecond DC/DC converter is connected to second terminals of all firstDC/DC converters in a first DC/DC converter set corresponding to thesecond DC/DC converter, a second terminal of each second DC/DC converteris connected to a first interface of the electrical energy storagesystem, the first interface is configured to receive a direct currentfrom a power generation system or output a direct current to the powergeneration system.
 2. The system according to claim 1, wherein whenVinv−Vbus>Vth and a battery pack is discharged, the second DC/DCconverter is configured to boost Vbus to output Vinv; or whenVinv−Vbus>Vth and a battery pack is charged, the second DC/DC converteris configured to buck Vinv to output Vbus, wherein Vinv represents arated voltage of the second terminal of the second DC/DC converter, Vbusrepresents a rated voltage of the first terminal of the second DC/DCconverter, and Vth represents a preset threshold voltage.
 3. The systemaccording to claim 1, wherein when −Vth<Vinv−Vbus<Vth, the second DC/DCconverter works in a direct mode, wherein Vinv represents the ratedvoltage of the second terminal of the second DC/DC converter, Vbusrepresents the rated voltage of the first terminal of the second DC/DCconverter, and Vth represents the preset threshold voltage.
 4. Thesystem according to claim 1, wherein when Vinv−Vbus<−Vth and the batterypack is discharged, the second DC/DC converter is configured to buckVbus to output Vinv; or when Vinv−Vbus>Vth and the battery pack ischarged, the second DC/DC converter is configured to boost Vinv tooutput Vbus, wherein Vinv represents the rated voltage of the secondterminal of the second DC/DC converter, Vbus represents the ratedvoltage of the first terminal of the second DC/DC converter, and Vthrepresents the preset threshold voltage.
 5. The system according toclaim 1, wherein when Vbus>Vbat and the battery pack is discharged, thefirst DC/DC converter is configured to boost Vbat to output Vbus; orwhen Vbus>Vbat and the battery pack is charged, the first DC/DCconverter is configured to buck Vbus to output Vbat, wherein Vbusrepresents the rated voltage of the first terminal of the second DC/DCconverter, and Vbat represents a rated voltage of an anode of thebattery pack.
 6. The system according to claim 1, wherein whenVbus=Vbat, the first DC/DC converter works in the direct mode, whereinVbus represents the rated voltage of the first terminal of the secondDC/DC converter, and Vbat represents the rated voltage of the anode ofthe battery pack.
 7. The system according to claim 1, wherein whenVbus<Vbat and the battery pack is discharged, the first DC/DC converteris configured to buck Vbat to output Vbus; or when Vbus<Vbat and thebattery pack is charged, the first DC/DC converter is configured toboost Vbus to output Vbat, wherein Vbus represents the rated voltage ofthe first terminal of the second DC/DC converter, and Vbat representsthe rated voltage of the anode of the battery pack.
 8. The systemaccording to claim 1, wherein the power generation system comprises aninverter, a first terminal of the inverter is connected to the firstinterface of the electrical energy storage system, and a second terminalof the inverter is connected to an alternating current load or analternating current power grid.
 9. The system according to claim 8,wherein the power generation system is a photovoltaic power generationsystem, the power generation system comprises a photovoltaic inverter,the photovoltaic inverter comprises a maximum power point tracking(MPPT) module and a DC/AC converter, and the inverter is the DC/ACconverter; and a first terminal of the DC/AC converter is connected tothe first interface of the electrical energy storage system, the firstterminal of the DC/AC converter is further connected to the MPPT module,and a second terminal of the DC/AC converter is connected to thealternating current load or the alternating current power grid.
 10. Anenergy storage system, wherein the system comprises an electrical energystorage system and a power generation system; wherein the electricalenergy storage system comprises M battery packs; M first direct currentto direct current (DC/DC) converters, wherein first terminals of the Mfirst DC/DC converters are respectively connected to the M batterypacks, the M first DC/DC converters are classified into N first DC/DCconverter sets, M is an integer greater than 1, and N is an integergreater than 0; and N second DC/DC converters, wherein the N secondDC/DC converters one-to-one correspond to the N first DC/DC convertersets, a first terminal of each second DC/DC converter is connected tosecond terminals of all first DC/DC converters in a first DC/DCconverter set corresponding to the second DC/DC converter, a secondterminal of each second DC/DC converter is connected to a firstinterface of the electrical energy storage system, the first interfaceis configured to receive a direct current from a power generation systemor output a direct current to the power generation system.
 11. Theenergy storage system according to claim 10, wherein when Vinv−Vbus>Vthand a battery pack is discharged, the second DC/DC converter isconfigured to boost Vbus to output Vinv; or when Vinv−Vbus>Vth and abattery pack is charged, the second DC/DC converter is configured tobuck Vinv to output Vbus, wherein Vinv represents a rated voltage of thesecond terminal of the second DC/DC converter, Vbus represents a ratedvoltage of the first terminal of the second DC/DC converter, and Vthrepresents a preset threshold voltage.
 12. The energy storage systemaccording to claim 10, wherein when −Vth<Vinv−Vbus<Vth, the second DC/DCconverter works in a direct mode, wherein Vinv represents the ratedvoltage of the second terminal of the second DC/DC converter, Vbusrepresents the rated voltage of the first terminal of the second DC/DCconverter, and Vth represents the preset threshold voltage.
 13. Theenergy storage system according to claim 10, wherein when Vinv−Vbus<−Vthand the battery pack is discharged, the second DC/DC converter isconfigured to buck Vbus to output Vinv; or when Vinv−Vbus>Vth and thebattery pack is charged, the second DC/DC converter is configured toboost Vinv to output Vbus, wherein Vinv represents the rated voltage ofthe second terminal of the second DC/DC converter, Vbus represents therated voltage of the first terminal of the second DC/DC converter, andVth represents the preset threshold voltage.
 14. The energy storagesystem according to claim 10, wherein when Vbus>Vbat and the batterypack is discharged, the first DC/DC converter is configured to boostVbat to output Vbus; or when Vbus>Vbat and the battery pack is charged,the first DC/DC converter is configured to buck Vbus to output Vbat,wherein Vbus represents the rated voltage of the first terminal of thesecond DC/DC converter, and Vbat represents a rated voltage of an anodeof the battery pack.
 15. The energy storage system according to claim10, wherein when Vbus=Vbat, the first DC/DC converter works in thedirect mode, wherein Vbus represents the rated voltage of the firstterminal of the second DC/DC converter, and Vbat represents the ratedvoltage of the anode of the battery pack.
 16. The energy storage systemaccording to claim 10, wherein when Vbus<Vbat and the battery pack isdischarged, the first DC/DC converter is configured to buck Vbat tooutput Vbus; or when Vbus <Vbat and the battery pack is charged, thefirst DC/DC converter is configured to boost Vbus to output Vbat,wherein Vbus represents the rated voltage of the first terminal of thesecond DC/DC converter, and Vbat represents the rated voltage of theanode of the battery pack.
 17. The energy storage system according toclaim 10, wherein the power generation system comprises an inverter, afirst terminal of the inverter is connected to the first interface ofthe electrical energy storage system, and a second terminal of theinverter is connected to an alternating current load or an alternatingcurrent power grid.
 18. The energy storage system according to claim 17,wherein the power generation system is a photovoltaic power generationsystem, the power generation system comprises a photovoltaic inverter,the photovoltaic inverter comprises a maximum power point tracking(MPPT) module and a DC/AC converter, and the inverter is the DC/ACconverter; and a first terminal of the DC/AC converter is connected tothe first interface of the electrical energy storage system, the firstterminal of the DC/AC converter is further connected to the MPPT module,and a second terminal of the DC/AC converter is connected to thealternating current load or the alternating current power grid.